Aqueous extracts of the feces of normal individuals have recently been found to degrade IgA type immunoglobulin molecules in such a way as to produce an Fc-like proteolytic fragment in addition to Fab fragments. Trypsin or other known intestinal proteases are unable to so degrade IgA, suggesting that additional enzymes or other proteolytic substances are present in intestinal content. The proposed research has as its objective the isolation and characterization of the proteolytic principal from intestinal contents and the isolation and characterization of the Fc fragment of IgA prepared with its use. The methods to be used for their study are molecular sieve and ion exchange chromatography, polyacrylamide gel electrophoresis, analytical ultra- centrifugation and immunologic techniques, e.g., Ouchterlony analysis, immunoelectrophoresis and antiserum production in animals. Bacterial cultures of fecal organisms will be studied in a search for the elaboration of the proteolytic substance. Feces of patients with disease states, e.g., inflammatory bowel disease, adult celiac disease, pernicious anemia and portal cirrhosis will be studied to evaluate the possibility that an abnormality in this proteolytic capacity may be related to the pathogenesis of these illnesses.